A cottage industry that has set up shop on the Internet meets the needs of parents who fear that their teens are using drugs — and also of teens who are afraid of getting caught.

Home drug test kits, along with sometimes wacky methods of circumventing them, are available online, and many sites sell both.

"It's a classic cat-and-mouse game," says Allen St. Pierre of the National Organization for the Reform of Marijuana Laws, or NORML. "I have seen it over and over. A drug test comes out, it's thwarted, then it's re-engineered, and it goes on and on."

Home drug tests range in price and sophistication from a $2.35 dip-strip urine test for THC, the active chemical in marijuana, to a $400 law-enforcement-style wipe test, which uses chemicals to detect drugs such as cocaine and methamphetamine on objects.

Psychemedics, a company that tests workers for drug use in corporations, government agencies and schools, markets a $59.95 hair analysis drug test to parents via the Internet. Parents snip off a lock of their teen's hair, send it to the Psychemedics laboratory and phone in for the results.

The test gives parents answers, but it also helps teens deflect peer pressure when confronted with drugs, says Raymond Kubacki Jr., president of Psychemedics. "They can say, 'Man, I'd like to try it, but my parents are testing and I'm going to get nailed,' " he says.

There are other options on the Internet for worried teens. Herbal cleansers like "Fast Flush" and "Absolute Detox" promise to wipe out any trace of drug use. Additives like "Urine Luck" can be mixed in to urine samples to throw off the results.

The $150 "Whizzinator," an anatomically correct urinating contraption, is worn under the pants and loaded with drug-free urine that a heating element keeps at body temperature. It comes in various skin tones and can be reused by ordering $12 syringes of dehydrated urine.

Dennis Catalano, owner of Puck Technology, the company that makes the "Whizzinator," would not answer questions about the product but says the goal is to help customers protect their rights.

"We believe that we have a right to privacy, and our bodily fluids are ours," he says.

But do these attempts to beat drug tests really work?

"Absolutely," says Sharon Levy, who specializes in childhood addiction at Children's Hospital in Boston. All drug tests can be thwarted, and enterprising teens and the companies that target them know how to do it, she says.

Drug tests also can come out negative even if a user is not trying to foil them and positive even if the teen has never used drugs, Levy says. "Home drug testing is like giving your daughter a home pregnancy test to find out if she has ever had sex," she says.

Levy is against home testing because she believes it can destroy the relationship between parents and their children. She also says testing at home may keep teens out of doctors' offices, where they can get help for a drug addiction.

But Sue Roche, president of the drug-prevention group National Families in Action, says parents are frustrated because pediatricians often will not test teens for drugs and may refuse to share the results with parents when they do test.

"If they tested a child for strep throat, do you think they wouldn't tell the parents? It's a grossly paradoxical situation," she says.

Levy says pediatricians often rely on more accurate means than drug tests to find out if a teen is in trouble. "The first thing you should do is talk to the child," she says.

And if a drug test is in order, let a physician do it, Levy says. "I'm sure I can do a better job with it than a parent can do at home."